In the near future Autonomous Robotic Systems (ARSs) will be playing an increasingly important role in space applications such as inspecting, repairing, refuelling and re-orbiting spacecraft. Recent interest into on-orbit proximity operations has pushed towards the development of autonomous Guidance, Navigation and Control (GNC) strategies. The proposed research will focus on each of these three aspects, with the goal of verifying innovative solutions. In particular, stereo vision navigation enables a wide variety of possibilities as it can provide information not only about the kinematic state, but also about the shape of the observed object. This technique relies on the acquisition and matching of the images taken from two cameras, on-board the ARS, in order to estimate the relative kinematic state between the ARS and a non-cooperative target satellite. The process of state estimation is carried out by means of a Kalman filter, which refines the state estimate in real time by merging the measurements taken from the images with the state propagation. Knowing the relative position, attitude and velocities with a certain degree of accuracy is of crucial importance for the ARS to track an optimal trajectory (output of the guidance block) in terms of propellant consumption and target¿s illumination conditions. At the scope of tracking this trajectory, a special application of the Impedance Control (IC) is proposed. This control algorithm is mainly applied to contact operations, with the goal of making the system behave as a mass-spring-damper group so to provide a compliant behaviour in response to an external forcing action. In the proposed version of the IC, the forcing term is replaced by a virtual force generated whenever the servicing spacecraft deviates from the reference trajectory. The final output of the research is to test and validate the described combination of stereo vision, optimal path planning and IC both from the numerical and experimental standpoint.
The field of space autonomous robotic mission for on-orbit servicing, inspecting, refuelling and dismissing has been widely studied in the last recent years. Many different mission architectures have been analysed and proved to accomplish the proposed mission goals. Moreover, some aspects of these studied have been put into practice during real space missions, thus testing their successfulness in real applications.
Despite the detailed level of investigation, the different aspects involved into autonomous operations have been mainly analysed separately from each other. In fact the focus switches between trajectory planning, visual navigation and optimal control strategies from research to research. It is therefore hard to understand whether is possible or not to summarize, unify and use these optimal strategies developed for each separated field in one mission.
As far as the present research concerns, stereo vision and impedance control have been separately used for different purposes proving their effectiveness in accomplishing the desired tasks. The novelty of the proposed research project consists in their combined use within the framework of autonomous on-orbit proximity operations which is a field becoming more and more appealing for future space missions. The team members will verify the effectiveness of the proposed approach to test the possibility of achieving remarkable improvements with respect to the other GNC strategies for autonomous satellite inspection and docking.